1. Field of the Invention
This invention relates to a waterproof casing and more particularly to a waterproof casing suitable for accommodating an electronic unit in an engine compartment in a vehicle.
2. Statement of the Prior Art
In the case of accommodating in a casing a device which must be waterproofed, a casing having a simple box like construction is unable to effect waterproofing of the device under an environment where the ambient temperature is subject to rapid changes. Since a pressure within the casing changes in response to a temperature change, the casing is deformed and water enters into the interior of the casing through clearances between a body and a cover for sealing the interior of the casing.
Heretofore, some waterproof casings which are used under such circumstances are known by Japanese Utility Model Public Disclosure Nos. 56-112978 (1981) and 57-186094 (1982). These casings are not formed into a sealed construction but they are provided with a vent hole in order to equalize the pressure in the interior and exterior of the casing. One casing disclosed in the former reference is provided with a labyrinth vent hole which retains water entering thereinto, while another casing disclosed in the latter reference is provided with a zigzag vent hole in which baffle boards are arranged in a zigzag manner in order to prevent water from entering into the interior of the casing.
One example of such a waterproof casing is that which may be used to protect an electronic control device for an engine from contamination with water when the device is disposed in an engine compartment. In such an engine compartment, the waterproof casing is subject to high temperatures generated by the engine and low temperatures from water which enters into the compartment during driving. In this case, the conventional waterproof casings have the following problems.
In the former casing the labyrinth vent hole can not hold a large amount of water while the zigzag vent hole in the latter casing can not baffle a high pressure of water.